International Civil Aviation Organization
WORKING PAPER / ACP-WGF15/WP23
26/05/06
AERONAUTICAL COMMUNICATIONS PANEL (ACP)
FOURTEENTH MEETING OF WORKING GROUP F
Cairo, Egypt 7 – 13 June 2006
Agenda Item 5: / AM(R)S spectrum requirements (Future Communications System (FCS))Bandwidth Requirements and Channelization Approaches for Future Airport Surface Communications in the 5091-5150 MHz Band.
(Presented by Robert Kerczewski, NASA Glenn Research Center)
SUMMARYThis paper extends the results of previous work in determining bandwidth requirements for future airport wireless surface communications. In particular, wake vortex sensing and information security requirements are described, as well as considerations for channelization of the 5091-5150 MHz band to accommodate future such systems currently being tested.
ACTION
The meeting is invited to consider the airport surface communications bandwidth requirements relative to AM(R)S allocations needed to support them.
Abstract
NASA, in cooperation with the FAA, industry, and academia, has been performing research and testing for a new generation of airport surface communications to enable advanced surface CNS systems and improved information distribution and provide lower cost, safer and more efficient airport surface operations. The key element is a wireless airport surface communications network, envisioned to operate in the 5091-5150 MHz band. Previous work has included assessment of communications requirements, characterization of channel performance in a dynamic airport environment, the development of channel models and simulations, waveform analysis, communications technology assessments, and airport surface network architecture definition. The next step is the development of an airport surface communications testbed, which is underway at the NASA Glenn Research Center and the adjacent Cleveland Hopkins International Airport. This paper will review communications requirements and present possible 5091-5150 MHz channelization schemes that will be evaluated in a prototype airport surface wireless communications testbed.
1 - Introduction
During the NASA Glenn Research Center (GRC) Space-Based Technologies (SBT) Project, research and development for next-generation airport surface communications networks was performed. The purpose was to develop and evaluate a wireless digital communications network that would enable deployment of advanced air traffic management systems required for safer and more efficient surface operations. Such systems include vehicle surveillance and weather sensors, navigation and landing, ATC voice and data, AOC voice and data, and surface management systems. Key reasons for the need to develop such a system include the requirement for increasing digital data flow on the airport surface to enable safe increases in traffic load; the need to communicate with mobile airport surface assets (requiring a wireless network solution); the increasing congestion on VHF communications channels; the high installation and maintenance cost of hard-wiring many new sensors at various locations on the airport surface; the vulnerability of underground communications links to cuts and service losses; and the need to integrate various types of data into an integrated network architecture.
NASA GRC’s research program for airport surface wireless communications, after the end of the SBT Project, is continuing through the NGATS-CNS National Testbed, described in another working paper. Work elements completed to date include:
· 5091-5150 MHz channel sounding campaign at CLE, BKL, MIA, FLL, and JFK airports (by NASA GRC, FAA and Ohio University)
· Development of 5091-5150 MHZ airport channel models for communications link optimization (by Ohio University)
· Analysis of technology alternatives for future ATC/AOC communications under the Eurocontrol/FAA Future Communications Study (by NASA GRC, ITT Industries, and QinetiQ)
· Study of communications requirements for a large airport (DFW) (by Trios/SAIC)
· Study of spectrum requirements for Airport Network and Location Equipment (ANLE) system (by Mitre Corp.)
· Analysis of interference compatibility of airport wireless network with satellite feeder links in the 5091-5150 MHz band (by Mitre Corp.)
· Development of NGATS-CNS National Testbed Design, including airport surface wireless network prototype testbed (by Sensis Corp and NASA GRC)
· Laboratory and field testing (at SYR) of prototype airport surface wireless network equipment (by Sensis Corp.)
· Laboratory testing of mobile network components (by NASA GRC)
This paper provides additional results regarding the development of the next-generation airport surface wireless communications system focusing on three areas: review and extension of data and bandwidth requirements analysis (to include wake vortex sensing and data security requirements); application of IEEE 802.16e standards to the airport surface wireless network architecture; and considerations for channelization of the 5091-5150 MHz band for airport surface wireless network use.
2.0 - High Level Concept of Use
It is forecasted that aviation will continue to grow at an anticipated rate of 3% annually. To meet the demand, modernization of surface operations and communications systems is necessary. The use of existing communications assets along with the implementation of new technologies will be required to meet increased capacity demands and maintain operational safety standards. A high level communications concept of use, rolled out in three stages, is summarized as follows.
Near Term:
§ Initially, the surface wireless communications network will meet fixed communication requirements. No mobility requirements are addressed with this initial version.
§ The communications system will initially transport a small number of critical systems which include ASDE-X. ASDE-X information will be transported from field sensors to the central processing system located at the Air Traffic Control Tower.
Mid Term:
§ Additional critical services are migrated onto the wireless network including Surveillance, Navigation, Communications and monitoring systems.
§ For large airport facilities, wireless and wired technologies operate in a hybrid configuration increasing the reliability and availability of services.
§ The wireless network enables System Wide Information Management (SWIM) availability to most SWIM native systems.
Far Term:
§ Mobility is added to the communications system. Communications directly to the aircraft is possible utilizing the full capabilities of the 802.16e standard.
§ Migration of VHF communications for ATC and AOC to 5091-5150 MHz band becomes possible.
3.0 – Application of IEEE 802.16e to Airport Surface Communications
The Eurocontrol-FAA Future Communications Study (FCS) performed assessments of technologies applicable to future air-ground communications for aviation. In the first phase of this study, a technology pre-screening effort conducted by ITT Industries for NASA in support of the FCS concluded that IEEE 802.16 standard was the best available technology alternative for airport surface communications:
“IEEE 802.16 provides the opportunity to utilize the MLS (extension band) spectrum to support a broad scope of communications needs, both data and voice, over the entire airport surface. Increased data rates on the airport surface that might not be met by a future system in the DME band, could be met by a fully COTS system base on 802.16e in the MLS (extension) band. The business case for 802.16 infrastructure may be driven by factors beyond ATS and AOC communications. For example, airport authorities may desire to support airport fixed services to support airport infrastructure. At current time, 802.16e mobility addresses mobile speed less than 120 km/hr and so will not support aircraft on landing and takeoff. This is an issue to address in future consideration of 802.16e for aeronautical applications.”
The IEEE 802.16 link-layer has many desirable properties for use in airport surface networking. The 802.16 specification has several configurable portions, some of which have implications on airport surface environments. Here we present initial results of examining the parameter profiles in the 802.16 specification which contain values that can be expected to be supported in equipment obtained in the near-term. The profiles in the protocol specification merely represent configurations that multiple vendors have agreed to support; the protocol's operation is not constrained to these values. However, having equipment custom-built is not feasible at this time, so current usage plans should involve parameters that are supported in the profiles.
The 802.16 specification offers 5 air interface options, but the only one that is appropriate for airport surface use is the WirelessMAN-OFDM option. The drivers for this determination are the desire to operate in the 5 GHz band (other options only operate above 11 GHz, or in unlicensed spectrum), and the desire for mesh mode operations to cover dead spots that may not be viewable from a single base station located at the tower. Other options only support the point-to-multipoint mode of operation, which would require multiple base-stations sited at various locations to specifically cover all of the dead spots from the tower. The mesh mode allows some subscriber stations to act as surrogate base stations to extend coverage. Mesh is more flexible and adaptable and is superior for the dynamic nature of the airport surface cnosidering its ability to support path diversity.
The physical (PHY) profiles for WirelessMAN-OFDM Mesh networks include 3, 3.5, 5.5, and 7 MHz channels. A channelization scheme can select combinations of these in order to reach the required aggregate data rates. There are also two duplexing options, TDD and FDD. These appear to be functionally equivalent, although TDD usage is more prevalent, with FDD intended mainly for low-cost subscriber stations that only support half-duplex operations.
Security considerations for 802.16 are discussed in the next section.
4.0 - Airport Surface Safety Communications Bandwidth Requirements
NASA GRC commissioned a study of airport surface communications requirements in 2004. The study was conducted by Trios Inc (now a part of SAIC Inc.) The study focused on a “level 12” US airport, Dallas-Forth Worth (DFW). The study, which analyzed current and planned communications loading for FAA air traffic operations, airline operations, and airport (port authority) operations, concluded that approximately 114 Mbps would be required to support all operations. Another WGF-15 working paper presented the methodology and results of this study.
Mitre Corporation extended this work in a 2006 study to estimate the total bandwidth required to implement a safety-related wireless local are network for the airport surface. Mitre concluded that the total bandwidth required was 60 MHz, assuming 20 MHz channel bandwidths. This analysis included a subset of the applications analyzed in the Trios/SAIC study, as well as some additional surveillance, automation and AOC data categories.
One additional future airport surface application which will present a significant data load to an airport surface communications network is wake vortex sensing. Researchers at NASA’s Langley Research Center are performing research and development on wake vortex detection systems and have provided the following information.
4.1 - Wake Vortex Data Throughput Requirements
To meet forecasted air traffic growth, research efforts aimed at reducing separation in the terminal airspace approach and departures are ongoing. To increase airport throughput, research in wake turbulence during arrival and departure stages of flight are being investigated. Accurate measurement of wake vortex turbulence will enable aircraft spacing based on actual wake vortex presence, rather than the more conservative procedures now in place using estimates of potential wake vortex based on aircraft type. The FAA and NASA are conducting tests and evaluation of wake vortex algorithms at Denver and St. Louis international airports. Airports with closely spaced parallel runways (CPRS) stand to benefit the most from this research effort. Reduced aircraft spacing will enable more all-weather use of existing runways. Furthermore, for airports that are “land locked”, it may be possible to increase the number of runways for a given amount of land.
To enable deployment of new wake detection technologies, communication systems that enable optimal wake sensor location at the airport are essential. Today’s wired airport communication media lack the flexibility required to deploy sensors at optimal locations. Wireless communications provide the data throughput and flexibility required to enable deployment of wake turbulence detection technologies. Wake turbulence detection communication requirements are:
· Air Traffic Control Tower to Sensor: 1.544 Mbps
· Air Traffic Control Tower to LIDAR: 20 Mbps
Communications to LIDAR is required for system optimization only and does not represent a continuous data requirement.
4.2 - Example Wake Detection System
Figure 1 shows an example Wake Detection System for a two runway configuration. It is anticipated that one system composed of two sensors will be required to detect wake turbulence for the entire airport facility. Each sensor requires communications to a central processor located at the Air Traffic Control Tower (ATCT).
The configuration shown in Figure 1 will require a total throughput of 3.088 Mbps.
Figure 1 – Example Work Vortex Turbulence Detection System
4.3 - Security Requirements
The use of wireless communications for certain safety critical applications will require sufficient security to be designed into the system. Table 1 indicates possible security level requirements for airport surface wireless network applications.
Table 1 – Airport Surface Communications Network Requirements Summary
Application Category / Application / Fixed or Mobile / Security Requirement - Network / Security Requirement - PhysicalSurveillance / · ASR-9 + Mode S
· ASR-11
· ASDE-X
· DBRITE / · Fixed
· Fixed
· Fixed
· Fixed / · High
· High
· High
· High / · High
· High
· Medium
· High
Weather / · LLWAS
· AWOS/ASOS
· TDWR
· ITWS
· WSP
· RVR
· Wake Vortex / · Fixed
· Fixed
· Fixed
· Fixed
· Fixed
· Fixed
· Fixed / · Medium
· Medium
· Medium
· Medium
· Medium
· Medium
· Medium / · High
· High
· High
· High
· High
· High
· Medium
Navigation and Landing / · ILS
· PAPI
· ALSF
· ATC Voice and Data / · Fixed
· Fixed
· Fixed
· Mobile / · Medium
· Medium
· Medium
· High / · High
· Medium
· Medium
· High
Automation / · CTAS
· ETMS / · Fixed
· Fixed / · High
· Medium / · High
· Medium
Electronic Flight Bag / · Software Loading
· Electronic Library Update
· Graphic Weather / · Mobile
· Mobile
· Mobile / · Medium
· Medium
· Medium / · Low
· Low
· Medium
AOC / · AOC voice and data / · Mobile / · High / · High
The network security requirement refers to requirements for ensuring that transmitted data remains sufficiently secure. In Table 1, High Network Security requires authentication, encryption, replay protection, anti-clogging; Medium Network Security requires authentication. Low Network Security would require no special measures, however all of the applications listed will require at least authentication.